The novel starts with the alien arriving at the earth. It doesn't have a physical body per se.

It has the ability to take over the mind of the host ( similar to the movie: The Host ).

What sets the novel apart is its brilliant plot. The alien takes over only if the person or **animal** is **asleep**. The Alien starts with taking over a cat then realises it's not the master, and eventually takes over the minds of humans. To leave to another host, the previous host must die. So, there's a lot of unexplained suicide.

The protagonist tries to stay awake but eventually he cannot.